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        FIT\METHOD Arg [Parameters ...]

    Select the line profile for fits. Five type of profiles are available.

      - GAUSS     Select gaussian profiles.
        Up to 5 Gaussian, dependent or independent can be fitted in a  spec-
        trum, according to command lines. Fitted parameters are:
            1) Area
            2) Velocity, and
            3) Width (FWHM)

      - SHELL     Horn-type profiles for Circumstellar Shells.
        Fitted parameters are:
            1) Area [K.MHz]
            2) Center offset [in MHz]
            3) Full Width at zero level, and
            4) Horn-to-center ratio (-1 for parabolic optically thick lines,
               0 for flat-topped lines, Infinity for perfectly double peaked
        Profiles  are  symmetric. Up to 5 dependent or independent lines may
        be fitted. X axis must be frequency.

      - NH3(1,1) or NH3(2,2) or NH3(3,3)
        Compute ammonia line profiles, with the assumptions of gaussian  ve-
        locity distribution and equal excitation temperatures. Fitted param-
        eters are:
            1) Main group opacity times ( Excitation temperature minus Back-
               ground temperature),
            2) Velocity,
            3) Width (FWHM = sqrt(8.0*alog(2.0)) * line 2nd order moment),
            4) Main group opacity.
        Up to 3 independent lines may be fitted. The hyperfine structure de-
        scription can be found in the structure HFS% right after the command
        METHOD is invoked.

      - HFS FileName    for HyperFine Structure
        This  is  very similar to the NH3 method, but the coefficients which
        describe the hyperfine structure are read in the file  FileName.  It
        must contain:
            - the number of hyperfine components (< 40, first line),
            - the  velocity offset and relative intensity (repeated for each
              component, one per line),
        The hyperfine structure description read from the this file  can  be
        found  in  the  structure HFS% right after the command METHOD is in-
        voked.  The fitted parameters are the same as for NH3 method.

      - ABSORPTION Filename   for hyperfine structures in absorption
        Fitted parameters are:
            1) One continuum level
        and for each line:
            2) Opacity
            3) Velocity, and
            4) Width (FWHM)

      - CONTINUUM [Width [Area_Ratio [Width_Ratio]]]  for Continuum drifts
        Fit a single gaussian and a linear baseline at the same  time,  with
        automatic determination of the parameters. Uses beam-switched infor-
        mation for two-component fitting if  required.  The  command  METHOD
        CONTINUUM  accept additional arguments, which can be used to custom-
        ize the fit:
            - Width is the width of the beam in  arc  seconds.  By  default,
              Width is a free parameter.
            - Area_Ratio  is the reference to main beam area ratio, used for
              beam-switch observing. By default, Area_Ratio is 1.
            - Width_Ratio is the reference to main beam  width  ratio,  used
              for beam-switch observing. By default, Width_Ratio is 1.
        A * can be used instead of a numerical value for each parameter, and
        indicates that the parameter is free.

    Note that in command LINES, one enters the peak line antenna temperature
    instead  of  the first variable in the guesses, except for SHELL method.
    Command LINES has no effect for CONTINUUM.

    CONTINUUM and GAUSS methods only are relevant for continuum data,  while
    GAUSS,  SHELL,  NH3, HFS and ABSORPTION methods can be used for spectro-
    scopic data.

Gildas manager 2020-10-13